The antireactive activity of glucosamine sulfate (GS) (CAS 29031-19-4) was tested in the rat in experimental models of subacute inflammation (sponge granuloma and croton oil granuloma), on subacute mechanical arthritis (kaolin arthritis) and in immunological-reactive arthritis and generalized inflammation (adjuvant arthritis). On these models GS was found effective in oral daily doses of 50-800 mg/kg. Tne potency of GS in comparison of that of indometacin used in the same tests as reference substance was found 50-300 times lower. Since, however, the toxicity of indometacin in chronic toxicity experiments is 1000-4000 times larger, the therapeutic margin with regard to prolonged treatments of inflammatory disorders results 10-30 times more favourable for GS than for indometacin. GS can therefore be considered as a drug of choice for prolonged oral treatment of rheumatic disorders.